1. Field of the Invention
The present invention relates to a microfilm search method and device which searches a desired frame by determining the presence of frames from a density change in the microfilm running direction.
2. Description of the Related Art
In a known microfilm search method, document or image marks (blips) are photographed or recorded beside the frames on microfilm and used as reference marks. The blips of microfilm during running are read and counted, and the blip count is used to identify frame addresses when a specific frame is sought. On the other hand, there is proposed a search method in which, instead of using the blips, the presence of frames is directly detected, and a desired frame is searched for from a sequence of detected frames.
In a case where the frames are detected as aforementioned, if the frame contains therein a portion having substantially the same density as that of an interspace of the frames (between the frames), this portion is incorrectly determined as between-frames. For example, when the microfilm is a negative film, a background portion in the frame on which an image or original document is photographed becomes black (non-transparent), while a peripheral portion surrounding the frame is white (transparent). When black characters or figures are depicted on a white background of the original, the character or graphic region becomes transparent (null) in the frame. Accordingly, if the presence of frames is determined from a density change on the microfilm, the transparent (null) portion other than a between-frame is incorrectly determined as between-frames. This causes an error in counting the number of frames, and therefore, correct frame search cannot be performed.